This invention relates generally to the fabrication of semiconductor components such as integrated circuits and wiring, and more particularly to an improvement in the polymer underlayer for MLR processes for definition of interconnection metallurgy. In more particular aspects it relates to pattern delineation on a substrate by simplified processes as a bi-layer structure utilizing a silylated or silicon-containing photoresist material overlying a polymeric coating on the substrate which polymeric coating has fluorine-containing segments in the polymer structural network.
A process simplification technique which offers a great deal of advantage over standard MLR process in fabrication of integrated circuits both in high density semiconductor and packaging technologies is one in which the photoresist mask is rendered O.sub.2 resistant by treatment with an organo-silicon reagent in solution or in vapor phase after resist patterning by standard process. The silylated resist mask is then used to pattern an underlying polymeric coating, which coating overlies the substrate by O.sub.2 plasma treatment as reactive ion etching. By using the silylation approach, a relatively thinner resist layer can be employed without the need of a separate mask layer since the silylated resist layer functions as an effective mask during O.sub.2 reactive ion etching (O.sub.2 RIE) of the underlying polymeric material to pattern-wise expose the substrate for subsequent deposition of interconnection metallurgy by lift-off. By using a thinner photoresist material a better and finer pattern definition can be obtained on the underlying polymeric material. Alternatively, process simplification can be provided by utilizing a silicon-containing radiation sensitive polymer layer as an O.sub.2 RIE resistant-imaging layer on the polymer underlayer. In this case, the pattern is defined in the top layer by standard lithographic techniques and then the resist pattern is replicated in the underlayer by O.sub.2 RIE when the silicon-containing layer functions as a mask. Such silylation techniques are known and described in U.S. Pat. No. 4,552,833; and U.S. patent application Ser. No. 720,781; U.S. patent application Ser. No. 713,370; U.S. patent application Ser. No. 713,509.
In the silylation process using the solution technique, the entire stack is immersed in the solution of the silylating reagent in a solvent which is selected such that a homogeneous solution of the organosilane is formed but none of the polymer film is eroded during silylation. For practical utility of this technique to provide necessary incorporation of the silicon moiety in the resin matrix, the resist layer must comprise a polymer phase having residual reactive functionality such as in the case phenolic resins (or novolac resins) and at the same time the underlying polymer must be inert and resistant to the silylation process. The conventional polyimides such as PMDA-ODA (pyromellitic dianhydride-oxydianiline), or Pyralin PI2540 available from E.I. duPont de Nemours Co. (hereinafter duPont) are found not suitable because these invariably lead to formation of non-removable RIE residue and also cannot be used for lift-off due to insolubility in common solvents after the polymers are cured to high temperature. On the other hand, use of soluble polyimides such as XU-218 of Ciba-Geigy is limited to thin films (less than 2-3u) since at greater thickness these films undergo cracking and crazing under silylation conditions involving solvent immersion processes.
Also the O.sub.2 reactive ion etching of these and other conventional prior art polymers as polysulfones of ICI Industries results in the formation of nonremovable RIE residues. With the use of solution silylation process, there has been the problem of RIE residues which could not be removed even after 50% to 70% over-etching. While this may take several forms, one resulting condition is known as "grass" formation. This is characterized by an unevenly etched polymer wherein there are thin stems of polymer extending upwardly from the otherwise exposed surface of the substrate beneath the etched polymer, giving it an appearance of "grass" growing from the surface of the substrate. Particles of silicon, embedded in these thin stems, appear to be the cause of this as well as other similar types of conditions wherein the surface has not been completely cleaned.
Such residues are undesirable as these interfere with substrate metal and/or metal-to-metal contacts in subsequent metallization steps resulting in multitude of problems including contact resistance and metal adhesion.